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Motor-Monitor/Vibration-Analysis Chips Have It All

Don Tuite | Dec 15, 2005

In designing wireless sensor network (WSN) machine monitoring and vibration analysis, the physical size of the sensor end-point modules must be minimized. To meet that goal, Quickfilter offers a monolithic four-channel alternative to using a DSP and supporting components for the edge-of-network filtering function.

The QF4A512 provides software-configurable input voltage ranges and gain settings for each channel. Its software-configurable anti-aliasing filters then handle signals from dc up to several hundred kilohertz. Next, it offers a software-configurable 16-bit analog-to-digital converter (ADC) and programmable digital filtering.

Each channel has an input range from dc to 1.0 MHz. The chip's tunable anti-aliasing filters (AAFs) implement a third-order Bessel function (linear phase) architecture. Cutoff is either 500 kHz or 3 MHz. A pipeline ADC that has a 12-bit ADC architecture follows the AAF.

However, the ADC can provide up to 16-bit resolution by oversampling the input and averaging the resultant conversions. And while the ADC can run up to 75 Msamples/s, achieving a 13.5-bit ENOB will limit designers to 1.17 Msamples/s.

Cascaded-integrator comb filters apply gain and offset correction. They also handle decimation/down-conversion of the oversampled data. Then, a set of cascaded-integrator half-band filters integrates to 16 bits and decimates to the desired sample rate.

Following that, each channel has its own user-programmable 512-tap digital finite-impulse response filter. Engineers can configure each filter as low-pass, notched low-pass, high-pass, band-pass, dual band-pass, band-stop, or dual band-stop.

Setup is via a GUI-based design tool that configures the complete signal path for all four channels and writes the information and filter coefficients to EEPROM on the chip. Reprogramming can take place in-circuit via the chip's serial-peripheral-interface bus interface.

The QF4A512 costs $9.89 each in quantities of 1000. Packaging is a 32-pin low-profile quad flat package. A full development kit is available for $199 online from the Quickfilter Web site or from Mouser (see the figure).